Structure and insertion properties of disordered and ordered LiNi0.5Mn1.5O4 spinels prepared by wet chemistry

We present the synthesis, characterization, and electrode behavior of LiNi_0.5Mn_1.5O₄ spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi_0.5Mn_1.5O₄ appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel Fd3m space group (SG)] and ordered spinel (P4 ₁ 32 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi_0.5Mn_1.5O₄ powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d⁸ metal for Mn in LiNi_0.5Mn_1.5O₄ oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi_0.5Mn_1.5O₄ cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ oxides are discussed.